US2566795A - Rotor wheel for centrifugal pumps - Google Patents

Description

Sept. 4, 1951 E. 56mm 2,566,795

ROTOR WHEEL FOR CENTRIFUGAL PUMPS Filed Dec. 18, 1.5M?

Q nvhmmBRRRa awstsa 88$ Patented Sept. 4, 1951 UNITED STATES PATENT OFFICE ROTOR WHEEL FOR CENTRIFUGAL PUMPS Emile Egger, Cressier, Switzerland Application December 18, 1947, Serial No. 792,553 In Switzerland December 20, 1946 6 Claims. 1

This invention relates to centrifugal pumps and particularly to rotor wheels thereof serving for the delivery of liquids which contain air or which froth or evaporate easily; for the delivery of thick substances of low to high concentration, substances with admixtures of fibrous, pasty and lumpy solid substances, as well as for the delivery of water with a high degree of efliciency.

The basic idea of the invention consists in choosing the sections of the blade passages of the rotor wheel so that the substance to be delivered moves away from the concave side of the blades so that a vacuum zone is created in the blade passages under the action of the fiow of the substance so that the rotor wheel is rendered insensitive to air thereby.

In the accompanying drawings Figs. 1 and 2 are diagrammatic vertical sections at right angles to one another of a constructional example of a pump rotor with three blades which iogether with two sets of curves in Figs. 3 and 4 will enable the invention to be understood.

Fig. 5 is a view similar to Fig. 1 of an open two-bladed rotor wheel.

Fig. 6 shows an arrangement particularly for dealin with liquids which froth freely.

Fig. 7 illustrates an embodiment with guide vanes in front of the entrance to the rotor wheel.

In Figs. 1 and 2, the width In of the outlet from the rotor wheel is so large that the passage between two blades I has the effect of an ejector, so that, as above-mentioned, in consequence of the flow of the liquid and the action of centrifugal force an increased vacuum is created in the blade passage.

The .form of the three blades I of the wheel depends not only on pure hydraulic considerations but has to be adapted to correspond to the material to be delivered. An object of the form given to the blades I is to produce a moving away of the stream of material to be delivered from the concave side of the blades.

The way in which the invention works explained with reference to Figs. 1 and 2 and also the curve Fig. 3 is as follows:

The rotor wheel requires first and foremost low liquid velocities, only the relative velocities in the rotor wheel itself being a determined factor. The velocity of entry at the entrance to the wheel must, if possible, not exceed 2 metres per second and have the same value as the velocities in the suction conduct. A great cross sectional area of the entrance 2 to the wheel results from this requirement.

figure for the velocities are only given by way of example and may, of course. vary within certain limits.

Under the action of the pressure of the atmosphere the liquid will be accelerated to the absolute velocity Us in the suction pipe corresponding to the vacuum produced in the pump. This imparted absolute velocity must be kept constant up to the entrance 2 to the rotor wheel, that is to say 17s=Ue. By slightly constricting the cross sectional areas in the rotor wheel up to the entrance edge 3 of the blade I a slight acceleration to the relative velocity Uer of the material to be A typical curve of the distribution of the rela delivered at this edge 3 is obtained.

By the enlargement of the outlet width bl of the rotor blade to suit the material to be delivered and the amplification of the cross sectional area of the blade passage aimed! at thereby, the relative liquid velocity var at the outlet 4 is very greatly reduced. The curve in Fig. 3 between De and var shows a smooth sinusoidal course for the relative velocities in the rotor wheel. This smooth shape is of great importance for the results obtained.

The ratio of the cross sectional area of the entrance 3 of the blade passage to the cross sectional area of the outlet 4 of the blade passage may rise from 1:10, the basic principle involved being that the greater the amount of air contained in a medium to be delivered is, or the more concentrated a thick substance to be delivered is, the greater the ratio chosen. must be.

By a reduction in the number of blades and/or by suitably shaping the blades I of the wheel the ratio can be very greatly varied (e. g. down to 1:05).

The rotor wheel shown in Figs. 1 and 2, while constructed in accordance with existing hydraulic principles, was given the form with the width of outlet b shown by the dotted lines and had to be provided with from seven to nine wheel blades.

One of the objects of the invention consists in the abovementioned attainment of a low relative outlet speed as a function of the greatly increased cross sectional area of the outlet 4 from the rotor wheel.

If it be supposed that the surface E of a liquid is set in rotation in the direction shown by the arrow in Fig. 1, this surface is subject to the laws of centrifugal force. It tends to emerge from the rotor wheel. The liquid which emerges must, however, be immediately replaced by liquid which follows it. However, in com sideration of the very enormous differences in the cross sectional area of the inlet 3 and the outlet 4 of the blade passages it is not possible for the liquid to become accelerated from the inlet to the blade to the outlet therefrom to such pump.

3 an extent that the liquid which emerges can be immediately replaced.

The following deduction follows therefore from this consideration:

The surface E of the liquid is ejected from the wheel by centrifugal force. Since the outlet 4 from the wheel is much too large in proportion to the inlet thereto, the liquid ejected cannot be completely replaced. Owing to this lack in the replacement, a moving away of the liquid from the concave side I2 of the blades occurs, i. e. a vacuum space R is formed which produces a considerably increased suctional action, so that an ejector action, which is a function of the particular choice of the cross sectional area, is consequently formed. The liquid stream does only touch the back of the blades.

It will now be understandable that liquids which contain air for example can be delivered without difiiculty. The air is drawn off by the action of the vacuum produced, without any very great adverse effect on the delivery output.

The present invention realizes the ideal combination of the centrifugal pump rotor wheel with the action of the rotor wheel of a water ring air In this way the penetration of the air into centrifugal pumps which has been feared hitherto is no longer inconvenient.

Owing to the small number of rotor blades and also to the large cross sectional area that exists in the blade passages it is possible to machine the surfaces of the blades and the inner surfaces of the wheel efiectively, thereby reducing the internal frictional resistance of the rotor wheel and improving the degree of hydraulic efficiency of the pump respectively.

The formation of a vacuum in the rotor wheel also prevents any cavitation effect therein.

Owing to the small surface tension due to the vacuum R, no vertexes occur.

Owing to the suctional or ejector action produced in the rotor wheel it is no longer necessary to endeavour to obtain a positive blade covering but it is specially necessary, when dealing with substances which contain air, to make the blade covering negative by the angle a. Any air that may have been carried in along with the liquid can only be expelled by centrifugal action by so doing.

Exhaustive experimental measurements have proved that in relation to the degree of hydraulic efficiency of a normally constructed rotor wheel the rotor wheel according to the invention is superior.

In Fig. 4 the lifting height in meters water col-' umn and the efficiency in per cent. are plotted against the delivery in liters/sec. The dotted lines belong to a low pressure rotor wheel of a well known construction and the full line curves to a rotor wheel according to the invention. The measurements were made under exactly identical conditions in the same pump casing. The data of the rotor wheel according to the invention used for these tests are:

Diameter of entry mm 150 Diameter of outlet mm 245 Number of blades 3 Ball passage mm 54 and of the rotor wheel of ordinary construction:

Diameter of entry mm 150 Diameter of outlet mm 245 Number of blades 7 Ball passage mm 17 The open rotor wheel shown in Fig. 5 has two blades 5. With this wheel it is possible, when dealing with liquids which containlarge quantities of air, to still further increase the effect obtained by the present invention. Owing to the open construction the axial thrust of the pump is also very greatly reduced, so that in most cases the provision of relief holes may be dispensed with. The action of the vacuum produced in the rotor wheel reduces the differences of pressure very considerably.

The delivery in hitherto used pumps of liquids which contain air and thick substances failed because the occluded and adherent air separated where the liquid or the thick substance entered the blades of the rotor wheel or at the outlet from the rotor wheel so that an air cushion formed in the pump casing, which reduced further conveyance if it did not stop it altogether.

The present invention eliminates these disadvantages. The liquid or the thick substance is drawn in in a much better way by the increased vacuum which is produced in the rotor wheel. The conversion of the energy of flow into pressure energy takes place in great part already in the rotor wheel. No conversion of kinetic into pressure energy in a diffuser becomes necessary, since the liquid leaves the rotor wheel with the pressure energy desired.

Hitherto, the delivery of frothing, saponaceous liquids or thick substances by means of centrifugal pumps ordinarily failed because the foam was driven ofi on the entrance of the liquid into the rotor wheel, after which a plug of foam formed on the suction side which stopped any further delivery by the pump.

The present invention enables the foam to be sucked within reach of the blades at a comparatively low speed, that is to say, to be drawn in directly, and the air to be taken into the vacuum zone, while the liquid, almost free from air, flows along the back of the blades. In cases where an enormous quantity of foam is, produced it is also possible to allow the pump embodying the invention, to run light, that is to say, the liquid entering it fills up only half the cross sectional area of entry of the suction branch, in which case an elfective removal of air from the pump on the suction side is produced. This case is illustrated in Fig. 6 which shows a pump 8 with a rotor wheel according to the present invention for liquids which froth strongly. As may be seen, a channel 6 supplies the material to the suction branch 1. This material only fills about half of the branch section. When a freely frothing liquid is to be delivered, the vacuum space (R in Fig. 1) collects the froth and an additional removal of air on the suction side through the upper portion of the branch 1 sets in also. Continuous Working free from shock thereby results.

Thick substances of high concentration present special difficulties to the conveyance thereof by means of centrifugal pumps. When highly concentrated the properties of the foreign substances, such for example as pulps, ground wood, potato pulp, spinach, tomato puree, and the like, replace the properties of the liquid almost entirely. Internal and external friction are increased considerably and the properties of the flow fall off in the same measure. In many cases a considerable percentage of the volume is air. In consequence of this, these thick substances become more or less elastic liquids or pastes which have quite different properties of flow to those of water. Their behaviour in normal centrifugal pumps shows that owing to their sluggishness and their friction such thick substances can no longer be compared with water.

If measurements with a pump of well-known type are made for water delivery, curve a in Fig. 4 is obtained for the lifting height plotted against the delivery. and the input may, for instance, amount to 5 H. P.

If measurements are made. with the same pumps for the delivery of thick substances, e. g. of paper pulp having a concentration of 6%, the lifting height is decreased to the curve d in Fig. 4 and the input is only 2 H. P. This phenomenon may be explained as follows: The path x-x in Fig. l of a water particle from inlet to outlet shows that this particle must be accelerated to the velocity desired in-a relatively short time. A water particle may in this time indeed be accelerated to the value desired. However, on delivery substances having properties quite different from water, tests have shown that the time available in pumps of known type is not sufficient, so that the input decreases very considerably.

In the rotor wheel according to the invention the time conditions are considerably modified with regard to prior wheels. The substance particle has much more time to be accelerated and leaves the wheel at an. Measurements with a wheel according to the invention have shown that the curve for thick substances is now so much higher than the curve d that the input is again H. P. Ideal conditions exist when the input for the delivery of thick substances is the same as for water.

The present invention meets the demands of these special features. By reason of its very large inlet cross sectional area and high vacuum the rotor wheel is able to bring even viscous thick substances within reach of the blades of the pump. The position of the inlet edges of the blades of the rotor wheel must correspond to the material which is to be conveyed. Once, however, the thick substance is in the blade passage its delivery is compulsory. The most important point in the delivery of thick substances is the bringing of the material to be delivered into the rotor wheel. Its further movement in the rotor wheel is then more a problem of transport than a pump problem.

Liquids which contain fibrous, pasty and lumpy solid substances require a formation of inlet and outlet edges and angles and also of the corresponding cross sectional area of the blades passages of the rotor wheel such as to stop any choking. up or stoppage of the inlet, cross sectional areas.

The present invention meets these demands also. Strongly profiled inlet edges of the blades without any dead corners and the one-sided admission of the blades in the rotor wheel prevent fibres from adhering. Large cross sectional areas of inlet, produced by the small number of blades, allow even large foreign bodies to pass through. In consequence of the comparatively low inlet and outlet velocities resulting from the corresponding inlet and outlet cross sectional areas, lumpy solid substances can be conveyed without damage. In this case also it is necessary to increase the suctional power of the pump considerably by increasing the vacuum.

When the casing is of spiral shape the novel rotor wheel requires a casing tongue which is carried close up to the rotor wheel. The cross sectional areas of the casing must be kept as large as possible so as to obtain low speeds particularly when thick substances are being dealt with.

Cal

An annular-casing with large cross sectional areas is, however, as advantageous as a spiral casing.

The rotor wheel according to the invention can be mounted, either horizontally or vertically, and the entrance of the material into the wheel can take place both radially or axially.

For the delivery of certain substances it is recommendable to provide a certain number (e. g.

three or four) of guide vanes 9 (Fig. 7) whichare fixed to the suction branch is ,and lie in front of the entrance 3 to the rotor wheel blades H.

When the rotor wheel according to the present invention is used it is not necessary to remove air from the casing of the pump previous to starting, for this wheel provides for automatic suction.

The rotor wheel according to the invention may also be used for water pumps: Owing to the small number of blades and the low velocities in the rotor wheel, losses due to friction are reduced and the over-all efficiency of the pump thereby increased. The angles of entry and outlet must be selected in such a way they will ensure that the water, for all deliveries, enters and leaves the rotor wheel with as little shock as possible.

If the manometric pressure produced in one single rotor wheel is not sufilcient, the pump may be built as a multistage pump, a rotor wheel according to the invention being built into the first stage as a priming or feed-in wheel. The remainin stages may be of the type of const uction well known hitherto. In this way, the advanta es of the present invention are imparted to high pressure pumps.

What I claim is:

l. A rotor wheel for a centrifugal pump, comprising in combination, a first ring-shaped impeller disc having an internal surface composed of a. substantially cylindrical surface delimiting an inlet opening, of a toroidal surface extending outwardlv from said cylindrical surface and of a generally conical surface extending from said toroidal surface; a second im eller disc coaxial with said first impe ler disc and being of approximate y the same outer diameter as the said first im eller disc, said second impeller disc having an internal surface formed by a surface of revolution located at a distance from the internal surface of the first impeller disc and pro ressing towards said inlet as the radius of the surface of revolution decreases, said distance decreasing gradually from said inlet opening to approximately the transition of said toroidal surface into said generally conical surface, and increasing from approximately this transition towards the periphery of the wheel; and a relatively small number of impeller vanes rigidly fixed to both of said impeller discs, said vanes being strongly curved towards the rear with regard to the direction of rotation of the wheel and arranged with regard to one another with a negative overlap, each of said vanes havin'r an inlet edge which, in extending from said toroidal surface to said second impeller disc, approaches the wheel axis, and said vanes having outlet edges located in the proximity of the outer periphery of said impeller discs.

2. The rotor wheel of claim 1, wherein each of said impeller vane is rounded at its inlet edge and becomes constantly thinner only outwardly of a point located away from said inlet edges by a distance at least equal to a third of the length of said vanes.

- 3. A centrifugal pump impeller comprising in combination, first and second impeller discs of approximately the same diameter coaxially located in spaced relation with respect to each other, said discs respectively having adjacent their peripheries opposite inner conical surface portions diverging in the direction of fluid flow through the impeller, said first impeller disc being formed with a central, substantially cylindrical opening passing transversely therethrough and forming an inlet for the impeller, and said first impeller disc having a curved ring-shaped surface portion located between and merging into said substantally cylindrical opening and said conical surface portion of said first impeller disc, said second impeller disc having an inner curved ring-shaped surface portion located opposite said curved surface portion of said first impeller disc and merging into said conical surface portion of said secondimpeller disc, and said curved surface portions gradually converging in the direction of fluid flow through the impeller up to the junction between said curved surface portion and said conical surface portion of said first impeller disc; and negatively overlapping impeller vanes fixed between said first and second impeller discs, each of said vanes having an outlet edge adjacent the peripheries of said impeller discs and an inlet edge extending from a first point on said curved surface portion of said first impeller disc to a point on said second impeller disc which is located nearer to the centers of said impeller discs than the edge of said inlet opening.

4. A centrifugal pump impeller comprising in combination two co-axial and spaced impeller discs having adjacent their peripheries opposite conical diverging surface portions, one of said impeller discs being formed with an axial entrance opening having an annular surface portion and with a curved surface portion merging along one edge into said annular surface portion and along its other edge into the conical surface portion of said one impeller disc, and the other of said impeller discs having in addition to its conical surface portion an inner curved surface portion merging into the conical surface portion of said other impeller disc, located .opposite said curved surface portion of said one impeller disc, and projecting into said annular entrance opening of the same; and a plurality of impeller vanes having a negative overlap and secured at opposite edges to said impeller discs, each of said vanes having an inner inlet edge extending between said curved surface portions of said impeller discs and an outer outlet edge extending between corresponding points of the peripheries of said impeller discs.

5. A centrifugal pump impeller arrangement comprising, in combination, first and second coaxial spaced discs having adjacent their periphcries opposite conical diverging surface portions, said first disc being formed with an axial entrance opening having an annular surface portion and with a curved ring-shaped surface portion merging along one edge into said annular surface portion and along its other edge into the conical 8 surface portion of said first disc, and said second disc having in addition to its conical surface portion an inner curved ring-shaped surface portion mergin into the conical surface portion of said second disc, located opposite said curved ring-shaped surface portion of said first disc, and projecting into said annular entrance opening of the same; and a plurality of impeller vanes having a negative overlap and being fixedly connected to at least one of said discs, each of said vanes haying an inner inlet edge extending between said curved ring-shaped surface portions of said discs and an outer outlet edge extending between corresponding points on the peripheries of said discs.

6. A centrifugal pump impeller arrangement, comprising in combination, first and second discs of approximately the same diameter coaxially located in spaced relation with respect to each other, said discs respectively having adjacent their peripheries opposite inner conical surface portions diverging in the direction of fluid flow through the impeller, said first disc being formed with a central substantially cylindrical opening passing transversely therethrough and forming an inlet for the impeller arrangement, and said first disc having a curved ring-shaped surface portion located between and merging into said substantially cylindrical opening and said conical surface portion of said first disc, said second disc having an inner curved ringshaped surface portion located opposite said curved surface portion of said first disc and merging into said conical surface portion of said second disc, and said curved surface portions gradually converging in the direction of fluid fiow through the impeller arrangement up to the junction between said curved surface portion and said conical surface portion of said first disc; and negatively overlapping impeller vanes fixedly connected to at least one of said discs, each of said vanes having an outlet edge adjacent to the peripheries of said discs and an inlet edge extending from a first point on said curved surface portion of said first disc to a point on said second disc which is located nearer to the centers of said discs than the edge of said inlet opening.

EGGER, EMILE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 21,756 Hibbard Oct. 12, 1858 678,223 Christian July 9, 1901 867,069 Neumann Sept. 24, 1907 1,050,698 Scheurmann Jan. 14, 1913 1,909,052 Froisland May 16, 1933 2,074,650 Holdaway Mar. 23, 1937 2,420,420 Durdin, Jr May 13, 1947 FOREIGN PATENTS Number Country Date 65,687 Austria 1913 82,191 Austria 1920 537,282 Great Britain 1941

Images